Diagnostic Performance of Carotid Contrast-Enhanced Ultrasound for Identifying Functionally Significant Coronary Artery Stenosis Assessed by Quantitative Flow Ratio: A Preliminary Prospective Study

Background: Carotid contrast-enhanced ultrasound (CEUS) provides a noninvasive means of assessing plaque vulnerability and may reflect the systemic burden of atherosclerosis. This study aimed to evaluate the diagnostic performance of carotid CEUS characteristics for identifying functionally significant coronary artery stenosis (CAS) defined by quantitative flow ratio (QFR). Methods: In this preliminary prospective study, 46 patients with suspected stable coronary artery disease who underwent carotid CEUS and coronary angiography with QFR assessment between September 2022 and November 2023 were enrolled. Patients were categorized into a QFR ≥ 0.80 group (n = 18) and a QFR < 0.80 group (n = 28). Carotid plaque burden, morphology, and CEUS-derived quantitative parameters were compared between groups. Univariate and multivariable logistic regression analyses were performed to identify independent factors associated with QFR < 0.80, and receiver operating characteristic (ROC) analysis was used to assess discriminatory performance. Results: Compared with patients with QFR ≥ 0.80, those with QFR < 0.80 had significantly higher mean intima-media thickness (IMT), larger plaque area, higher plaque-to-lumen enhancement ratios (Pmax/Cmax and Pmean/Cmean), and more vulnerable plaque features, including irregular margins and thin fibrous caps. In multivariable analysis, Pmax/Cmax (adjusted OR: 14.394, 95% CI: 2.718–76.220; p = 0.002) and mean IMT (adjusted OR: 7.740, 95% CI: 2.040–29.363; p = 0.003) remained independently associated with QFR < 0.80. ROC analysis showed that the combined model incorporating Pmax/Cmax and mean IMT achieved the best discrimination for QFR < 0.80 (AUC: 0.931, 95% CI: 0.845–0.989), with 78.6% sensitivity and 94.4% specificity. Conclusions: Carotid CEUS-derived plaque enhancement characteristics, particularly Pmax/Cmax, together with mean IMT, were independently associated with functionally significant CAS. These findings suggest that carotid CEUS may provide complementary, noninvasive information for vascular risk stratification, but it should not be considered a substitute for coronary angiography-based physiological assessment.